Transistors are extensively used as an important electronic device (electronic component) which constitutes televisions or computer equipment, and today, they are produced using inorganic substances such as silicon as a main material. Recently, an organic transistor (OFET) using organic substances as the transistor member (refer to Non Patent Document 1) has attracted attention. OFET is soft and flexible, and has an advantageous benefit in that raw materials of OFET can be produced at low cost per unit area since raw materials of OFET is inexpensive; therefore, OFET is considered to be an indispensible item for the make up of ubiquitous computing age, that is, an essential component for realizing flexible and low-cost terminals.
OFET is an electronic device which includes three electrodes, an insulating layer, and a semiconductor layer as essential members. An example of the device structure is shown in FIG. 1. Although a method for forming a gate insulating layer (GI), which corresponds to a reference number 3 in the FIGURE, includes a wet process such as a printing method and a dry process such as vacuum deposition or sputtering, the wet process is preferable to lower the cost (refer to Non Patent Document 2). Meanwhile, usually, it is necessary for the wet process to go through a superheating (sintering) process after the film is produced. When flexible materials having a low heat resistance temperature are used for substrates, it is required for the superheating (calcination) process to be conducted at a lower temperature. For example, when polyethylene naphthalate (PEN) is used for a substrate, the calcination temperature needs to be 150° C. or lower. Also, when the printing method is applied to the wet process, it is required for ink which is used for forming an insulating film to have an excellent printing property in order to facilitate the formation of a fine pattern.
Meanwhile, among various properties required for the GI itself, there are properties which concern a device production process, and properties which concern the electric property (FET property) of a device. As an example of the former, there is a property of insolubility to a solvent (that is, solvent resistance) which is used for an organic semiconductor layer placed on the GI. As an example of the latter, it is considered that, in the state of a thin film, the higher the insulating property (leakage current is small) and degree of surface smoothness, the more the device property is improved. As materials for forming the insulating film, for example, a polyvinylphenol-based material (I) using polyimide-based materials as a curing agent is known (refer to Non Patent Document 3); also, polyvinylphenol-based materials using melamine-based resins as a curing agent are known (refer to Non Patent Document 4).
These materials need to be processed with high-temperature calcination at about 200° C., and, usually, the materials are used when glass material is used as the substrate. However, since a feature of the materials is flexibility, it is difficult for it to be applied to a plastic substrate having a low heat resistance temperature. In order to skip the high temperature calcination process, a thermoplastic resin (II) represented by polyraethylmethacrylates and polystyrenes is also known (refer to Non Patent Document 5). However, the thermoplastic resin has poor solvent resistance, and it is difficult to laminate a conductive layer, a semiconductor layer, and the like on the thermoplastic layer by the printing method; therefore, the dry process which needs facilities for deposition or the like is required. In addition, a solid or liquid type bisphenol general-purpose epoxy resin (III) is also known (refer to Non Patent Document 6). However, it is known that an insulating film formed from this material has a large amount of leakage current. In Patent Document 1, insulating materials including a silane coupling agent and an epoxy resin are disclosed (refer to Patent Document 1). Although in Patent Document 2, a method for producing a circuit device by a letterpress plate reverse printing method is disclosed, there is no disclosure regarding low-temperature calcination (refer to Patent Document 2). Accordingly, there is no ink technique for forming an insulating film which is sufficiently equipped with an insulating property, solvent resistance, and a calcination temperature to form an electronic device by providing the insulating film on a flexible substrate. Also, in the current circumstances, there is no ink technique for forming the insulating film which has sufficient ability for forming a fine pattern.